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Stratospheric Processes And their Role in Climate
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Stratospheric Processes And their Role in Climate
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| Home | Initiatives | Organisation | Publications | Meetings | Acronyms and Abbreviations | Useful Links |
SPARC is a research project established in 1992 by the Joint
Scientific Committee of the WCRP (World Climate Research Programme), who recognized the role played by the
stratosphere in the climate system. While intense research was and continues to be carried out on stratospheric
ozone depletion, there were important areas that were not receiving sufficient attention, notably those concerning
the role of the stratosphere in a changing climate and the feedback of climate change on the stratosphere. The mandate
of SPARC is to stimulate research in those areas that require its attention.
SPARC deals with the role of stratospheric dynamical, chemical and radiative processes in the global climate of
the troposphere-stratosphere system. The key scientific issues has been identified as follows: the influence of the
stratosphere on climate, the physics and chemistry associated with stratospheric ozone decreases, stratospheric
variability and its monitoring, and UV irradiation changes.
The SPARC’s activities have been structured within the three following themes:
The stratosphere-troposphere system is changing due to both natural and anthropogenic factors, and the challenge is to understand the system sufficiently well to predict future scenarios. The test of this understanding lies in explaining past changes, but these changes need to be adequately quantified. To this end, SPARC has conducted three major assessments on temperature, ozone, and water vapour. These results have been used in the Scientific Assessment of Ozone Depletion 1999, and in the IPCC-Third Assessment Report 2001. Trends in dynamical activity would also be crucial to determine the overall climate effects of stratospheric changes
The dynamical, chemical and radiative processes which occur in the stratosphere all influence climate. An assessment of the current knowledge of these processes has shown that research is needed to better understand the following important topics: Upper troposphere/lower stratosphere processes, Gravity wave processes and the parameterisation of the effects of unresolved internal gravity waves in global numerical atmospheric models, Dynamical coupling between the stratosphere and the troposphere.
In order to verify our current understanding of the role of the stratosphere in climate and to better assess future climate change, general circulation models including a detailed representation of the stratosphere are essential. SPARC through GRIPS (GCM-Reality Intercomparison Project for SPARC) has studied how well the current generation of these models simulates the current climate and its variability. In order to make a meaningful comparison with data, a comprehensive observed climatology of the means and variability of basic stratospheric parameters has been assembled.
The activity foreseen for SPARC in the future will aim to understand the observed stratospheric trends of temperature, ozone and water vapour, and solar effects, through modelling studies. These would be particularly aimed at elucidating UT/LS variability and its role in the overall climate system by building on the modelling work carried out in the stratospheric temperature trends study and GRIPS. New SPARC initiatives on stratospheric data assimilation and UV radiation penetration will be undertaken. Within this framework described in more detail below, the main priority for SPARC is to continue to facilitate research on stratospheric processes and their role in climate by providing a forum or umbrella for international co-operation and encouraging inter-disciplinary exchanges.
With the availability now of a sizeable body of information on the parameters of relevance describing stratospheric changes over the last two decades, it is appropriate to ask the following scientific questions:
The principal motivation arises from the fact that, over the period from the late 1970s to 2000, a number of changes, some dramatic, have been witnessed in the stratospheric climate: changes in ozone that are not the same from one decade to the next; aerosols from two volcanic eruptions perturbing the chemical and radiative budgets; water vapour data that indicate changes of various sorts depending on the times considered; pronounced temperature changes but with varying trends over the low and the middle and high latitudes, punctuated by sharp transient warmings in the aftermath of the volcanic eruptions; solar irradiance changes conforming to the 11-year cycle variations; variations in stratospheric circulation; and climate changes in the Arctic and Antarctic stratospheres especially during the winter-spring seasons.
Additional motivation arises from the fact that the coupling of the stratospheric and tropospheric climatic states is gathering increasing interest. The possibility that the tropospheric modes of variability may be related to stratospheric ones, and vice versa, is of considerable significance for climate change in the overall Earth system. Thus, a SPARC-centred focus on understanding stratospheric change could have a direct bearing on changes from the upper troposphere down to the surface.
The answers to these questions would also constitute useful inputs to the IPCC and WMO assessments. SPARC is uniquely placed to tackle the questions.
SPARC maintains strong links with the other WCRP projects concerned with different aspects of the climate system, as well as with IGBP and IHDP projects, as the expert community on the atmosphere in the vicinity of the tropopause and above. Particularly noteworthy is the co-operation with IGAC (International Global Atmospheric Chemistry) project of the IGBP as some of the research interests of SPARC on the upper troposphere-lower stratosphere region overlap with those of IGAC.
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Last update: July 04, 2001